1. Field of the Invention
The present invention relates to an optical integrated circuit (IC) and method for manufacturing the same and, more particularly to, such an optical IC and method for manufacturing the same that can reduce a scatter loss of an optical signal.
2. Description of the Related Art
In a conventional optical IC practically used in optical pick-up or optical-fiber communication, typically an optical element such as a lens is used to guide a light which has propagated a space, to then detect it by a photo-detector.
Such a optical IC, however, is expected to be of a wave-guide path type so as to reduce the number of the optical elements used therein and hence the costs thereof as well as to have more functions by use of, for example, an electro-optic effect. FIG. 7 is a cross-sectional view for showing one example of a configuration of a wave-guide path type photo-detector which is manufactured on the optical IC substrate. As shown in FIG. 7, on the substrate of the optical IC, to avoid erroneous detection of stray light which hit a portion other than a photo-detector formed on the substrate to detect an optical signal which has propagated a space, to block light, typically a light-blocking film layer made of metal such as aluminum is provided at the portions other than the photo-detector. Moreover, avoid corroding of this light-blocking film layer, it is typically sandwiched by insulator film layers.
A wave-guide path type photo-detector construction by use of an optical IC substrate having such a configuration, however, has suffered from a problem that, as shown in FIG. 7, an insulator film layer and a light-blocking film layer are formed as stacked on the substrate to thereby form a steep step with a value on the micrometer order at a boundary between a photo-detecting portion and such a portion of the light-blocking film layer that surrounds the photo-detecting portion, so that the resultant bent portion has a large radiation loss of the light propagating an optical wave-guide layer.
Furthermore, since this step is step, a clad layer is liable to be cracked at its step portion, which constitutes another problem.
Further, to polish such a steep step at the boundary of the light-blocking film layer for improvement of the performance, the costs are increased, which constitutes a further problem.
Those problems become more remarkable as the numbers of the insulator film layers and the light-blocking film layers increase when the optical IC employs a multi-layer wiring configuration.
It is therefore an object of the present invention to provide an optical IC and method for manufacturing the same that can reduce the scatter loss of an optical signal easily and inexpensively.
The above object of the present invention can be achieved by an optical integrated circuit provided with: a photo-detector formed on a substrate; at least one light-blocking film layer which is formed in a portion of a main surface of the substrate other than the portion where the photo-detector is formed; at least two insulator film layers which are formed so as to cover the light-blocking film layer; a clad layer which is formed consecutively over the light-detector and the insulator film layers; and an optical wave-guide path layer formed on the clad layer, wherein the clad layer is formed in a smooth slope toward the photo-detector.
According to the present invention, the clad layer is formed as a smooth slope, so that the wave-guide path layer can have a smooth slope (that is, smooth step structure) formed thereon, to thereby guide a light with a low loss. It also makes it possible to reduce the scatter loss of an optical signal at the bent portion of the light-blocking film layer.
In one aspect of the optical integrated circuit of the present invention, the insulator film layers form a plurality of staircase-like steps, each of which has a horizontal length measuring at least xc2xd of a maximum film thickness of the light-blocking film layer. Namely, each of the steps is formed in an interval measuring at least xc2xd of a maximum film thickness of the light-blocking film layer.
According to this aspect, the inclination of the steps in a staircase is made moderate, so that the step can be buried smooth, to thereby form such an optical wave-guide path layer that has an even smoother slope (that is, smooth step structure).
In another aspect of the optical integrated circuit of the present invention, the insulator film layers each have a film thickness measuring at least ⅓ of the maximum film thickness of the light-blocking film layer.
According to this aspect, the inclination of the steps in a staircase is made moderate, so that the step can be buried smooth, to thereby form such an optical wave-guide path layer that has an even smoother slope (that is, smooth step structure).
In further aspect of the optical integrated circuit of the present invention, the insulator film layer have an inclined face having an inclination angle smaller than 90 degrees toward the photo-detector.
According to this aspect, the inclination of the steps in a staircase is made moderate, so that the step can be buried smooth, to thereby form such an optical wave-guide path layer that has an even smoother slope (that is, smooth step structure).
In further aspect of the optical integrated circuit of the present invention, the lowest one of the insulator film layers is formed so as to cover the photo-detector.
The above object of the present invention can be achieved by an optical integrated circuit provided with: at least one night-blocking film layer which is formed in a portion of a main surface of the substrate other than the portion where the photo-detector is formed; at least two insulator film layers which are formed so as to cover the light-blocking film layer; a clad layer which is formed consecutively over the light-detector and the insulator film layers; and an optical wave-guide path layer formed on the clad layer, wherein the insulator film layers form a plurality of staircase-like steps toward the photo-detector.
According to the present invention, a multi-layer film underlying the clad layer is adapted to form, in construction, steps in a staircase at the boundary between the photo-detector and any other portions, so that when the clad layer is formed thereon, the optical wave-guide path layer can have a smooth slope (that is, smooth step structure) formed thereon, to thereby guide light with a low loss. It also makes it possible to reduce the scatter loss of an optical signal at the bent portion of the light-blocking film layer.
Furthermore, it is unnecessary to polish the steep step at the boundary of the light-blocking film layer for improvement of the performance, so that this steep step at the boundary of the light-blocking film layer can be smoothed only by etching, thus manufacturing the optical IC simply and inexpensively.
In one aspect of the optical integrated circuit of the present invention, each of which has a horizontal measuring at least xc2xd of a maximum film thickness of the light-blocking film layer.
According to this aspect, the inclination of the steps in a staircase is made moderate, so that the step can be buried smooth, to thereby form such an optical wave-guide path layer that has an even smoother slope (that is, smooth step structure).
In another aspect of the optical integrated circuit of the present invention, the insulator film layers each have a film thickness measuring at least ⅓ of the maximum film thickness of the light-blocking film layer.
According to this aspect, the inclination of the steps 10 in a staircase is made moderate, so that the step can be buried smooth, to thereby form such an optical wave-guide path layer that has an even smoother slope (that is, smooth step structure).
In further aspect of the optical integrated circuit of the present invention, the insulator film layer have an inclined face having an inclination angle smaller than 90 degrees toward the photo-detector.
According to this aspect, the inclination of the steps in a staircase is made moderate, so that the step can be buried smooth, to thereby form such an optical wave-guide path layer that has an even smoother slope (that is, smooth step structure).
In further aspect of the optical integrated circuit of the present invention, the lowest one of the insulator film layers is formed so as to cover the photo-detector.
The above object of the present invention can be achieved by a method for manufacturing an optical integrated circuit provided with: a process of forming at least one light-blocking film layer in a portion of a main surface of a substrate other than the portion where a photo-detector is formed; a process of forming a insulator film layer having a staircase-like step so as to cover the light-blocking film layer toward the photo-detector; a process of forming a clad layer having a smooth slope by pouring a liquefied derivative material prepared to have appropriate viscosity onto the staircase-like step; and a process of forming an optical wave-guide path layer on the clad layer.
According to the present invention, the optical IC of the present invention can be manufactured.